Heavy chains are often used for lifting, dragging, or stabilizing extremely heavy loads. Such heavy load-bearing chains are used in dragline mining operations where the chain is used to hoist and drag the bucket, in marine applications where the chain is used in mooring or anchoring large sea vessels, and in other applications where the chain is exposed to high pull loads and/or external wear conditions. When a link in such a load-bearing chain fails or wears out, a coupling link (i.e., a link that can be assembled for installation and disassembled for removal) can be used as a temporary or permanent repair of the chain, i.e., to replace the broken or worn link. The installation and removal of coupling links, however, typically occurs in the field under less than ideal conditions.
In dragline operations, a large bucket is suspended from a boom by an arrangement of cables, hoist chains and rigging components, and is pulled through the ground, toward the dragline machine, by way of cables and drag chains. Chain for dragline operations is usually made by casting each link in-situ around an adjacent link. In this way, there are no joints or welds in any of the links so as to provide enhanced strength and durability. Coupling links are used with these chains to connect them to the dragline bucket and to replace worn or broken chain links.
The drag chain and hoist chain are put under considerable load and are subjected to adverse wear conditions. For example, hoist chains for large dragline buckets may be loaded up to as much as 1,000,000 pounds. Drag chains are not only put under very high loading, but are also subjected to high levels of abrasion and impacts as the drag chains are often pulled along and through the ground during a digging operation. The coupling links must be able to withstand the same loads and conditions. Unexpected breakage or premature wearing out of a chain link can result in economic loss with downtime for the excavating machine and, in some cases, a hazard to workers.
Coupling links are prone to suffering premature failures and short life spans. Moreover, in efforts to withstand the rigors of digging, coupling links have included various retainers to hold the components of the coupling link together. The retainers, however, are generally difficult to remove on account of earthen fines, distortion of the parts, corrosion, etc. They also typically require a hammer for both installation and removal, which can impose safety hazards to the workers.